Aezotropic compositions of 1,1,1,4,4,4-hexafluorobutane and n-pentane and the use thereof in the production of foams

ABSTRACT

An azeotropic composition made up of from about 73 to about 87% by weight of 1,1,1,4,4,4-hexafluorobutane and from about 13 to about 27% by weight of n-pentane is used as a blowing agent in a process for the production of polyurethane foams.

BACKGROUND OF THE INVENTION

The present invention relates to novel azeotropic compositions, aprocess for the production of foams in which these azeotropiccompositions are used and to foams produced using these azeotropiccompositions.

The use of trichloromonofluoromethane (CFC-11) and otherchlorofluorocarbons as blowing agents in the production of urethanefoams is well known. These CFC blowing agents are also known to have anadverse effect upon the ozone layer in the atmosphere. The urethane foamindustry is therefore investigating methods for producing foams withgood physical properties without using CFC blowing agents.

Initially, the most promising alternatives appeared to behydrogen-containing chlorofluorocarbons (HCFCs). U.S. Pat. No.4,076,644, for example, discloses the use of1,1-dichloro-2,2,2-trifluoroethane (HCFC-3) and1,1-dichloro-1-fluoroethane (HCFC-141b) as blowing agents for theproduction of polyurethane foams. However, HCFCs also have some ozonedepletion potential. There is therefore mounting pressure to findsubstitutes for the HCFCs as well as the CFCs.

Alternative blowing agents which are currently considered promisingbecause they contain no ozone-depleting chlorine are fluorocarbons (FCs)and partially fluorinated hydrocarbons (HFCs). The use of1,1,1,4,4,4-hexafluorobutane as a blowing agent is disclosed inLamberts, "1,1,1,4,4,4-hexafluorobutane, a New Non-Ozone-DepletingBlowing Agent for Rigid PUR Foams", Polyurethanes World Congress 1991(September 24-26), pages 734-739.

U.S. Pat. No. 4,898,893 teaches that a blend of a liquid hydrocarbon andhalogenated hydrocarbon is useful as a blowing agent for the productionof isocyanurate foams.

The use of mixtures of a chlorofluorocarbon having a boiling pointbetween 74° and 120° F. and an alkyl alkanoate having a molecular weightof no more than 88 as a blowing agent for foams is disclosed in U.S.Pat. No. 4,960,804. HCFC-123 and HCFC-141b are among thechlorofluorocarbons disclosed therein.

U.S. Pat. No. 5,035,833 discloses the use of a mixture ofdichlorotrifiuoroethane and at least one paraffin having 5 or 6 carbonatoms as blowing agents useful for the production of rigid polyurethanefoams.

U.S. Pat. No. 5,096,933 discloses a process for the production of rigidpolyurethane foams in which cyclopentane and/or cyclohexane andoptionally a low boiling compound (i.e., boiling point less than 35° C.)with no more than 4 carbon atoms which is homogeneously miscible incyclopentane and/or cyclohexane is used.

Azeotropes of HCFCs and various compounds and azeotropes of organiccompounds which may be used in combination with HCFCs have also beendescribed in the prior art as being useful blowing agents for theproduction of foams.

U.S. Pat. No. 4,900,365, for example, teaches that azeotropes of adichlorotrifiuoroethane and isopentane are useful in the production ofpolyurethane foams.

U.S. Pat. No. 5,106,527 discloses the use of azeotropes of 2-methylbutane and 1,1-dichloro-1-fluoroethane as blowing agents for theproduction of rigid, closed cell foams.

The azeotropic mixtures taught in U.S. Pat. No. 5,166,182 must haveboiling points below 50° C. These azeotropic mixtures are formed fromorganic compounds having surface active properties that enable theblended azeotropic mixture to become miscible with polymer resins.Examples of the organic compounds described as being useful in theproduction of such azeotropes include: n-pentane, acetone, methylalcohol, methyl formate, ethyl formate, ethyl alcohol, 2-methyl butane,nitromethane, cyclopentane, 2,3-dimethyl butane, 2,2-dimethyl butane anddimethyl sulfide. These azeotropes may be used in combination withfluorocarbons but an azeotrope in which a fluorocarbon is one of thecomponents is not taught or suggested.

U.S. Pat. No. 5,227,088 discloses azeotrope-like compositions which aremade up of 1-chloro-3,3,3-trifluoropropane and a hydrocarbon containingfive or six carbon atoms.

U.S. Pat. No. 5,283,003 discloses a blowing agent which is made up of atleast one five-carbon member hydrocarbon, a chlorinated alkane andmethyl formate. Methylene chloride is the preferred chlorinated alkane.

Azeotropic mixtures in which HCFCs are included are also known to beuseful as cleaning solvents. U.S. Pat. No. 4,055,507, for example,discloses an azeotropic mixture of 1,2-dichloro-1,1-difluoroethane and3-methylpentane which is taught to be useful as such a solvent. Japanese1,141,995 discloses an azeotropic mixture of 67 to 87% by weight ofHCFC-123 and 13 to 33% by weight of 2-methyl butane which is useful as acleaning solvent. Japanese 1,141,996 discloses an azeotropic mixture ofHCFC-141b and n-pentane or 2-methyl butane or 2,2-dimethyl butane whichis also taught to be useful as a cleaning solvent.

The use of azeotropes formed from specified amounts of1,1,1,4,4,4-hexafluorobutane and n-pentane as a blowing agent or acleaning solvent has not, however, been described in the prior art.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide novel azeotropiccompositions.

It is a further object of the present invention to provide an azeotropiccomposition which contains no chlorine and therefore has an ozonedepletion potential of zero.

It is also an object of the present invention to provide a process forthe production of urethane foams in which no chlorine-containing blowingagent is employed.

It is another object of the present invention to provide polyurethanefoams having good physical properties, which foams are produced withoutthe use of a chlorine-containing blowing agent.

These and other objects which will be apparent to those skilled in theart are accomplished with the azeotropic compositions of the presentinvention. These azeotropic compositions are made up of from about 73 toabout 87% by weight of 1,1,1,4,4,4-hexafluorobutane and from about 13 toabout 27% by weight of n-pentane. These azeotropic compositions areincluded in a foam-forming mixture which includes an isocyanate andisocyanate-reactive material. The foams made with these azeotropiccompositions are characterized by good physical properties.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a graph showing a plot of the mole fraction of n-pentanein the vapor phase versus the mole fraction of n-pentane in the liquidphase of various mixtures of n-pentane and 1,1,1,4,4,4-hexafluorobutanerefluxing at steady state at one atmosphere.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an azeotropic composition which isparticularly useful for the production of rigid foams. This azeotropiccomposition may also be used for solvent cleaning applications. Moreparticularly, the present invention is directed to azeotrope-likecompositions consisting essentially of from about 73 to about 87% byweight of 1,1,1,4,4,4-hexafluorobutane (based on the total weight of theazeotropic composition)(i.e., from about 54 to about 74 mole %) and fromabout 13 to about 27% by weight of n-pentane (based on the total weightof the azeotropic composition) (i.e., from about 26 to about 46 mole %).

The compounds which are essential to the compositions of the presentinvention are n-pentane (boiling point=35.5° C.) and1,1,1,4,4,4-hexafluorobutane (boiling point=24.6° C.).1,1,1,4,4,4-hexafluorobutane is also known by those skilled in the artas R-356 or HFC-356 mffm. A process for producing1,1,1,4,4,4-hexafluorobutane is disclosed in U.S. Pat. No. 5,315,047.The n-pentane used in the compositions of the present invention may beof normal commercial purity, i.e., at least 95% n-pentane.

The composition made up of from about 73 to about 87% by weight1,1,1,4,4,4-hexafluorobutane and from about 13 to about 27% by weightn-pentane is azeotropic in nature in that compositions within theseranges exhibit a substantially constant boiling point. Because they havesuch a substantially constant boiling point (18.5° C. at oneatmosphere), the mixture does not tend to fractionate to any greatextent upon evaporation. After evaporation, only a small differenceexists between the composition of the vapor phase and the initial liquidphase. This difference is so small that the compositions of the vaporand liquid phases are considered to be substantially identical.Therefore, any mixture within the above-noted ranges exhibits propertieswhich are characteristic of a true binary azeotrope.

The azeotropic compositions consisting essentially of from about 77 toabout 84% by weight 1,1,1,4,4,4-hexafluorobutane and from about 16 toabout 23% by weight n-pentane are particularly preferred azeotropiccompositions. The composition consisting essentially of 80% by weight1,1,1,4,4,4-hexafluorobutane and 20% by weight n-pentane has beenestablished, within the accuracy of the calibration procedure describedbelow, as the true binary azeotrope with a boiling point of about 18.5°C.

The drawing shows a graph on which the mole fraction of n-pentane in thevapor phase is plotted against the mole fraction of n-pentane in theliquid phase of varying mixtures of n-pentane and1,1,1,4,4,4-hexafluorobutane refluxing at steady state and at oneatmosphere. These mole fractions were obtained by gas chromatography andwere adjusted to be quantitative by using a calibration curve as isdescribed more fully below. The point at which the mole fraction curvecrosses the line with a slope of 1 and intercept 0 is, by definition,the true binary azeotropic composition.

The calibration curve used to calibrate the gas chromatographic resultswas generated as follows. A series of blends of n-pentane with1,1,1,4,4,4-hexafluorobutane was prepared with from 0 to 100 molepercent of n-pentane in 10% increments. The mole percent of1,1,1,4,4,4-hexafluorobutane in each blend was the difference between100 mole percent and the mole percent of n-pentane. First, each blendwas injected into a Gas Chromatograph ("GC") to establish a correlationbetween relative peak areas versus actual molar concentrations. This wasdone by making duplicate samples of each blend and measuring each sampletwice. This data was used to establish the calibration curve and a 95%confidence interval which was used to establish the range of error forthe azeotropic compositions.

The relative molar amounts of 1,1,1,4,4,4-hexafluorobutane and n-pentanenecessary to form an azeotropic composition were then determined by atwo step process. In the first step of this process, n-pentane alone wascharged to the reactor. Subsequently, 1,1,1,4,4,4-hexafluorobutane wasadded to the reactor in increments indicated by the datapoints in thegraph. After each addition of 1,1,1,4,4,4-hexafluorobutane, the contentsof the reactor were allowed to reflux for 10-15 minutes with the refluxcondenser at 0° C. and open to the atmosphere through a drying tube.After steady state was achieved, samples of the liquid and vapor weretaken through sample ports. The temperature of the liquid in the reactorwas measured and the vapor temperature was measured at a point betweenthe reactor and the condenser. Duplicate samples were injected into theGC and the relative peak areas were recorded. These relative peak areasconverted to mole fractions using the calibration curve.

In the second step, 1,1,1,4,4,4-hexafluorobutane was charged to areactor. Subsequently, n-pentane was added in increments indicated bythe datapoints in the graph. The contents of the reactor were thenheated and samples were taken and analyzed in the same manner as wasdone in the first step. The data generated in each of the first andsecond steps was plotted with the resultant graph being shown in thedrawing.

An azeotrope is defined as a mixture of liquids where, at the boilingpoint, the concentration of the components is the same in the liquid andvapor phases. The point at which the mole fraction plot crosses the linehaving a slope of 1 and an intercept of 0 is the expected azeotropiccomposition.

The azeotropic compositions of the present invention are particularlyuseful as chlorine-free blowing agents for the production of closedcell, rigid foams. Foams made with the azeotropic compositions of thepresent invention have low densities comparable with those of foamsproduced with higher amounts of R-356 alone and relatively lowK-factors.

Foams may be produced with the azeotropic compositions of the presentinvention by reacting a) an isocyanate-reactive material with b) anorganic polyisocyanate in the presence of one of the azeotropiccompositions of the present invention, optionally in the presence of acatalyst and/or other additives and processing aids.

Any of the known organic isocyanates, modified isocyanates orisocyanate-terminated prepolymers made from any of the known organicisocyanates may be used to produce foam from the azeotropic compositionsof the present invention. Suitable isocyanates include aromatic,aliphatic, and cycloaliphatic polyisocyanates and combinations thereof.Useful isocyanates include: diisocyanates such as m-phenylenediisocyanate, p-phenylene diisocyanate, 2,4-toluene diisocyanate,2,6-toluene diisocyanate, 1,6-hexamethylene diisocyanate,1,4-hexamethylene diisocyanate, 1,3-cyclohexane diisocyanate,1,4-cyclohexane diisocyanate, hexahydrotoluene diisocyanate and itsisomers, isophorone diisocyanate, dicyclohexylmethane diisocyanate,1,5-naphthalene diisocyanate, 1-methylphenyl-2,4-phenyl diisocyanate,4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate,4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylenediisocyanate and 3,3'-dimethyl-4,4'-biphenylene diisocyanate;triisocyanates such as 2,4,6-toluene triisocyanate; and polyisocyanatessuch as 4,4'-dimethyl-diphenylmethane-2,2',5,5'-tetraisocyanate and thepolymethylene polyphenyl polyisocyanates.

Undistilled or crude polyisocyanate may also be used. The crude toluenediisocyanate obtained by phosgenating a mixture of toluene diamines andthe diphenylmethane diisocyanate obtained by phosgenating crudediphenylmethanediamine (polymeric MDI) are examples of suitable crudepolyisocyanates. Suitable undistilled or crude polyisocyanates aredisclosed in U.S. Pat. No. 3,215,652.

Modified isocyanates are obtained by chemical reaction of diisocyanatesand/or polyisocyanates. Modified isocyanates useful in the practice ofthe present invention include isocyanates containing ester groups, ureagroups, biuret groups, allophanate groups, carbodiimide groups,isocyanurate groups, uretdione groups and/or urethane groups. Preferredexamples of modified isocyanates include prepolymers containing NCOgroups and having an NCO content of from about 25 to about 35% byweight, preferably from about 28 to about 32% by weight. Prepolymersbased on polyether polyols or polyester polyols and diphenylmethanediisocyanate are particularly preferred. Processes for the production ofthese prepolymers are known in the art.

The most preferred polyisocyanates for the production of rigidpolyurethanes are methylene-bridged polyphenyl polyisocyanates andprepolymers of methylene-bridged polyphenyl polyisocyanates having anaverage functionality of from about 1.8 to about 3.5 (preferably fromabout 2.0 to about 3.1) isocyanate moieties per molecule and an NCOcontent of from about 25 to about 35% by weight, due to their ability tocrosslink the polyurethane.

Any of the known isocyanate-reactive compounds may be used to producefoams from the azeotropic compositions of the present invention.Polyether polyols are preferably used to produce rigid foams inaccordance with the present invention. Amine-initiated polyether polyolshaving functionalities of from about 3 to about 4 and molecular weightsof at least about 149, preferably from about 149 to about 1500, mostpreferably from about 300 to about 800 are particularly preferred. Theseamine-based polyols may be prepared by reacting an amine, polyamine oraminoalcohol and optionally other initiators (with or without water)with propylene oxide and optionally, ethylene oxide, in the presence ofan alkaline catalyst. The product is then treated with an acid,preferably a hydroxy-carboxylic acid to neutralize the alkalinecatalyst. U.S. Pat. No. 2,697,118 discloses a suitable process for theproduction of such amine-initiated polyols.

Examples of suitable amine initiators include: ammonia, ethylenediamine, diethylene triamine, hexamethylene diamine, amines such astoluene diamine, and aminoalcohols. Aminoalcohols, particularly,monoethanolamine, diethanolamine, and triethanolamine are preferredinitiators.

It is preferred that the amine initiator be reacted with propyleneoxide, although it may also be reacted with ethylene oxide. If used, theethylene oxide may be used in an amount of up to 100% by weight of thetotal alkylene oxide used. The propylene oxide is generally used in anamount of from about 40 to about 100% by weight of the total alkyleneoxide employed, preferably from about 60 to about 100% by weight. Thetotal amount of alkylene oxide used is selected so that the productpolyol will have an average molecular weight of at least about 149,preferably from about 149 to about 1500.

The amine-based polyether polyol is included in the foam-forming mixturein an amount of from about 20 to about 70% by weight, based on the totalfoam forming mixture, preferably from about 40 to about 50% by weight.

Other polyether polyols (i.e., polyether polyols which are not based onan amine) known to be useful in the production of rigid polyurethanefoams as well as polyester polyols may also be used in the practice ofthe present invention. Combinations of an amine-initiated polyol andpolyols which are not based upon amines are particularly preferred. Whensuch mixtures are used, the amine-initiated polyol is generally includedin an amount of at least 20% by weight, preferably from about 50 toabout 80% by weight.

When amine-initiated polyol is based upon an aminoalcohol, polyesterpolyols having functionalities of from about 2 to about 3 (preferablyfrom about 2 to about 2.5) and molecular weights of from about 180 toabout 900, preferably from about 300 to about 600 are preferablyincluded in the polyol mixture in an amount of from about 5 to about50%, most preferably from about 15 to about 35% by weight of the totalamount of polyol.

Any of the catalysts known to be useful in the production of rigidpolyurethane foams may be employed in the practice of the presentinvention. Tertiary amine catalysts are particularly preferred. Specificexamples of suitable catalysts include: pentamethyl-diethylene triamine,N,N-dimethyl-cyclohexyl amine, N,N',N"-dimethylamino-propyl-hexahydrotriazine, tetramethylene diamine, tetramethyl-butylene diamine, anddimethylethanolamine. Pentamethyl-diethylene triamine,N,N',N"-dimethylamino-propyl-hexahydro triazine, andN,N-dimethyl-cyclohexyl amine are particularly preferred.

Materials which may optionally be included in the foam-forming mixturesof the present invention include: chain extenders, crosslinking agents,surfactants, pigments, colorants, fillers, antioxidants, flameretardants and stabilizers. Carbon black is a preferred additive.

Any of the known methods for producing polyurethane foams may be used inthe practice of the present invention. Suitable methods include reactionof the various reactants using the known one-shot process, prepolymerprocess or semi-prepolymer process.

Having thus described our invention, the following Examples are given asbeing illustrative thereof. All parts and percentages given in theseExamples are parts by weight or percentages by weight, unless otherwiseindicated.

EXAMPLES

The following materials were used in the Examples:

POLYOL A: A 630 OH number polyol prepared by reacting 1 mole of ethylenediamine with 5 moles of propylene oxide.

POLYOL B: A 250 OH number polyol prepared by reacting 1 mole of glycerinwith approximately 3.3 moles of propylene oxide.

R-356: 1,1,1,4,4,4-hexafluorobutane.

n-Pent: n-pentane.

Tegostab B-8426: A polysiloxane polyether copolymer which iscommercially available from Goldschmidt Chemical Corporation.

DMCHA: dimethylcyclohexylamine.

ISO: The polymethylene polyphenyl polyisocyanate prepolymer having anNCO content of approximately 27% which is commercially available fromMiles Inc. under the name Mondur E-577.

EXAMPLE 1

19.91 parts of R-356 and 4.98 parts of n-Pent were first mixed. Thismixture was then blended with the other components listed in TABLE 1under B-SIDE. (The materials and the amount of each of those materialsincluded in the B-SIDE are given in TABLE 1.) ISO was then mixed withthe B-SIDE (in the amount indicated in TABLE 1) in a mixing vessel usingan air driven stirrer. After 5 seconds of mixing, the reaction mixturewas poured into a polyethylene-lined cardboard box which measured10"×10"×2.5". The reactivity time, density and K-factor of the foamproduced were determined. The results of these determinations arereported in TABLE 1.

EXAMPLE 2 (COMPARATIVE)

The procedure of Example 1 was repeated using the same materials withthe exception that only R-356 was used as the blowing agent. Thespecific materials, the amount of each material and the characteristicsof the product foam are all reported in TABLE 1.

                  TABLE I                                                         ______________________________________                                                        EXAMPLE 1                                                                              EXAMPLE 2                                            ______________________________________                                        B-SIDE                                                                        POLYOL A, pbw     50.67      49.56                                            POLYOL B, pbw     50.67      49.56                                            Tegostab B-8426, pbw                                                                            2.24       2.20                                             Water, pbw        2.24       2.20                                             DMCHA, pbw        3.70       3.26                                             R-356, pbw        19.91      30.75                                            n-Pent, pbw       4.98       --                                               A-SIDE                                                                        ISO, pbw          165.58     162.06                                           RESULTS                                                                       Mix Time, sec.    5          5                                                Cream Time, sec.  <10        <10                                              Gel Time, sec.    46         46                                               Density, lbs/ft.sup.3                                                                           1.86       1.82                                             K-Factor (BTU-in./°F. hr.ft.sup.2)                                                       0.133      0.127                                            ______________________________________                                    

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A process for the production of a polyurethanefoam comprising reacting a polyisocyanate with an isocyanate-reactivematerial in the presence of an azotropic composition consistingessentially ofa) from about 73 to about 87% by weight of1,1,1,4,4,4,-hexafluorobutane and b) from about 13 to about 27% byweight of n-pentane.
 2. The azeotropic composition of claim 1 consistingessentially ofa) from about 77 to about 84% by weight of1,1,1,4,4,4-hexafluorobutane and b) from about 16 to about 23% by weightof n-pentane.
 3. The azeotropic composition of claim 1 consistingessentially ofa) about 80% by weight of 1,1,1,4,4,4-hexafluorobutane andb) about 20% by weight of n-pentane.
 4. The process of claim 1 in whichthe polyisocyanate is selected from polymethylene polyphenylpolyisocyanates and prepolymers of polymethylene polyphenylpolyisocyanates.
 5. The process of claim 1 in which theisocyanate-reactive material is selected from amine-initiated polyetherpolyols.
 6. The process of claim 1 in which the polyisocyanate is aprepolymer of a polymethylene polyphenyl polyisocyanate.